Anodized surfaces of metal products made of metals including aluminum, zinc, magnesium and titanium and alloys thereof have been marked and decorated for many years by dyeing and sealing selected areas of the anodized surface. Conventionally decorated soft anodized surfaces are not sufficiently durable and are therefore not favored for inner shock absorber tubes and other uses in which the anodized surface is subjected to frictional sliding contact with bearings, bushings and the like since the outer wear surface of the tube must be very smooth and the application of shock position markings thereto by conventional techniques such as application of decals or labels, and ink printing results in slightly raised marking surfaces on the tube which rapidly wear off as do other non-permanent patterns such as decals and surface markings provided by other techniques. Also, it is known that various colors and dyes applied to anodized surfaces may fade or discolor, particularly when used outdoors.
Since high strength and low weight are particularly important in many applications such as tubular metal cycle frames and parts, the hard high strength 7000 Series aluminum alloys are preferred over softer alloys such as the 2000, 5000 or 6000 Series aluminum alloys.
Metal articles having a hard anodized surface with a smooth surface pattern comprised of durable visible markings of contrasting color are therefore desired.